| The relationships between pressure, temperature, structure, and diffusion in crystalline, molten and vitreous silicates have been investigated with molecular dynamics computer simulations, vibrational (Raman and infrared) spectroscopy, and chemical diffusion experiments.;Three compositions which represent simple model compositions for the silicate-dominated regions of the Earth were examined with the molecular dynamics technique. SiO;Model predictions for ambient condition structures agree well with experimental observation indicating that the ab-initio potentials used in the simulations accurately reflect the bonding between silicon, magnesium and oxygen in these phases. Pressure effects on diffusion coefficients are also consistent with experimental data. The dominant compression mechanism in polymerized melts is closure of the intertetrahedral (Si-O-Si) angle to a 40 percent decrease in molar volume. Gradual increases in coordination number for all ions occur. The Si;Molecular dynamics simulations have been used to calculate the properties of forsterite (Mg;Raman and mid-infrared spectra of the glasses MgSiO;Experiments designed to obtain diffusion rates of aluminum, magnesium, and calcium in melts along the diopside-anorthite join have been carried out. (Abstract shortened with permission of author.). |
